Golf balls are classified into two types. One is thread wound golf balls which comprise a thread wound core and a cover covering the core, and the other is solid golf balls, e.g. one-piece solid golf balls which are integrally composed of rubber and two solid golf balls which are composed of a rubber core and a cover thereon.
The solid golf balls contain at least one rubber portion. The rubber portion has been prepared from a rubber composition which mainly contains as base rubber butadiene rubber or a mixture of butadiene rubber and the other rubber (e.g. natural rubber and isoprene rubber). The base rubbers, however, have some problems in processability (for example, mixing process or extruding process), thus resulting in poor production efficiency. These problems are more serious when a polybutadiene having high Mooney viscosity or narrow molecular weight distribution is used to improve the physical properties of golf balls.